Bracing with my right hand, I use my middle finger on my left hand to open up to maybe 1 Kg. After that I'll use both my fore and middle finger. Fore, middle and ring finger for 3 - 4 Kg. I have never thought about using my thumbs. I have seen people do it. Should give it a try.

When I cleared out the space for my small studio, I found a 2' x 2' mirror.
I set it on a couple buckets in front of the wheel and propped it up against the wall.
Works great. I pretty sure I got the idea to do that from one of Simon's videos.